The present disclosure relates to a system and method for selectively limiting power of an engine. More particularly, the present disclosure relates to a system and method which uses an adjustable position exhaust valve to power limit the engine to reduce the likelihood damage to the engine when certain fault conditions occur.
Two-stroke engines, particularly those used in snowmobile or other cold weather vehicle applications, create a unique set of challenges for controlling the power output capability of the engine to protect the engine during both present fault states and anticipated fault states. These two-stroke engines have highly tuned exhaust systems. Exhaust temperature has of a significant impact on both trapping and scavenging efficiency. Therefore, traditional soft engine speed/power limiters with progressive increment/decrement strategies operate with mixed success. The implementation of such engine speed/power limiters often results in a loss in vehicle momentum which is very noticeable to the driver.
A conventional approach for limiting engine speed and power is to reduce the engine speed by stopping the fuel and or ignition signal such that an entire engine cycle is missed and the engine is merely motored. This mechanism can be implemented in a progressive nature such that the frequency and pattern of missed cycles changes if the fault is not removed or the power and/or engine speed is not reduced significantly enough to protect the engine.
Modern high specific power two-stroke engines operate very close a detonation limit at a high power output. This forces engine calibrations to reduce power output so that there is a suitable stability margin on the lean side of a calibration window to account for engine production tolerances and range of fuel composition and fuel quality on the market today. As such, with a missed cycle engine speed limiter, when the ignition is removed and then reinstated it can introduce both a significant change in exhaust temperature as well as a detonation even at the point of reinstatement due to the significant change in ignition timing over the course of a very small number of cycles.
The system and method of the present disclosure uses a multi-state active exhaust system which limits engine power that is used in conjunction with or in place of a traditional, multi-severity soft engine speed limiters. Having active control of the exhaust valve position allows for a maximum valve position to be adjusted on the fly to change the effective size of an exhaust port. Changing exhaust port size alters a maximum engine speed and power output while being less intrusive to the rider than the use of a missed cycle engine speed limiter.
In one embodiment of the present disclosure, an active exhaust valve position control provides a plurality of discrete mechanical valve states for positioning an exhaust valve. Detection of system faults causes an electronic control unit to adjust the exhaust valve between the discrete mechanical valve states in order to adjust the size of the exhaust port and limit engine power.
In another illustrated embodiment of the present disclosure, the active exhaust valve position control provides a plurality of intermediate positions between the discrete mechanical valve states. In this embodiment, large severity events cause the system to adjust the valve position between the discrete mechanical valve states, while low severity events adjust the exhaust valve position incrementally between the discrete valve states without changing the current valve state. In yet another illustrated embodiment of the present disclosure, the frequency of the low severity events impacts the maximum valve state by means of a non-dimensional weighting factor or a direct linear frequency threshold conditional dependency on either the intra state steps or the discrete valve state position steps.
The system and method of the present disclosure provides active manipulation of engine speed and/or engine power output by reducing the size and timing of an exhaust port of the engine. Unlike conventional missed cycle speed limit control strategies, the system and method of the present disclosure does not attempt to operate the engine in modes substantially different from the normal, non-fault operation. The system and method of the present disclosure relies of the exhaust port limiting to reduce the power capacity, volumetric efficiency and engine speed of the engine in the same manner that would occur if the exhaust port was smaller than designed. Therefore, the engine reduces airflow capacity for the given smaller exhaust port. In effect, the engine operates completely normal in this state, the only difference being that the operating window (engine speed and power) is reduced. The initiation of the speed/power limiter of the present disclosure is less intrusive to the driver while the power is reduced by the same amount as conventional power limiters.
According to an illustrated embodiment of the present disclosure, a method for selectively reducing power of an engine having at least one piston movable in a cylinder and an exhaust port includes providing an exhaust valve in communication with the exhaust port of the engine. The exhaust valve has an adjustable position to change an effective size of the exhaust port. The method also includes sensing a condition likely to cause damage to the piston of the engine, and adjusting a position of the exhaust valve to reduce a size of the exhaust port in response to sensing the condition likely to cause damage to the piston of the engine, thereby limiting power of the engine.
According to another illustrated embodiment of the present disclosure, an engine includes at least one piston movable in a cylinder, an inlet port, an exhaust port, and an exhaust valve in communication with the exhaust port. The exhaust valve has an adjustable position to change an effective size of the exhaust port. The engine also includes a sensor configured to sense a condition likely to cause damage to the piston of the engine, and an engine control coupled to the sensor. The engine control unit is configured to adjust a position of the exhaust valve to reduce a size of the exhaust port in response to sensing the condition likely to cause damage to the piston of the engine, thereby limiting power of the engine.
Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the invention as presently perceived.
Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure.